You can set a filter on the Subject line and then have the message forwarded to your device as a Level 1 message.

You can then assign a different tone for L1 messages to differentiate them from regular emails.

Not sure if that's a sufficient solution to your specfic needs, but it's an option nonetheless.

For example, we have a global filter set up which looks at the subject line for the word 'urgent'.
If 'urgent' appears in the subject, it is automatically flagged as a Level 1 message, and thus gets a different alert notification on the handheld.